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Observations of the Galactic center 511 keV lineA review of observations of the positron annihilation 511 keV line from the Galactic center and plane is presented. Emphasis is given to the new data from balloon observations in 1988 and 1989. The positron annihilation source in the direction of the center was found to be turned on again in 1988 October after being observed in a quiescent state since the early 1980s. There is evidence for variability between May and October in 1988. The new observations give the first data in which the line is spectrally resolved and in which the Galactic center and plane components of the annihilation radiation are independently measured. These data support the two-component model of the emission with a variable point source near the center and a steady-state source distributed along the galactic plane. Comparing measurements of narrow and wide field instruments in the 1980s gives a flux of about 8 x 10 exp -4 photons/sq cm/s for the point source in its high state and a flux of about 1.2 x 10 exp-3 photons/sq cm/s/rad for the galactic plane component with a relatively flat distribution over the central radian. The line width for the point source component is about 3 keV FWHM.
Document ID
19920060996
Acquisition Source
Legacy CDMS
Document Type
Conference Paper
Authors
Gehrels, Neil
(NASA Goddard Space Flight Center Greenbelt, MD, United States)
Date Acquired
August 15, 2013
Publication Date
January 1, 1991
Subject Category
Astrophysics
Meeting Information
Meeting: International Symposium on Gamma-Ray Line Astrophysics
Location: Paris
Country: France
Start Date: December 10, 1990
End Date: December 13, 1990
Accession Number
92A43620
Distribution Limits
Public
Copyright
Other

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